This invention relates to an ultrasonic diagnostic apparatus which has a prove formed of transducer elements arranged on a plane in two-dimensional directions and scans, i.e., transmits and receives, ultrasonic beams emitted from these transducer elements in two-dimensional directions to collect three-dimensional information on a body under inspection. The invention relates more particularly to an ultrasonic diagnostic apparatus of this kind having a probe made up of an electrostrictive material which is capable of improving reliability and image quality and reducing the production cost thereof.
An electronic linear scan type ultrasonic diagnostic apparatus conventionally used in wide application fields, as shown in FIG. 18, employs a probe 2 made up of a plurality of narrow rectangular transducer elements 1 arranged in columns. Among these transducer elements 1, a particular group is solely selected by electronic switches 3 each coupled to each of the transducer elements 1 to connect the same to a transmitting and receiving section. Each time such groups of the transducer elements thus selected are sequentially changed, a transmitting pulse generator 4 applies to each of the transducer elements 1 a high voltage pulse to emit an ultrasonic beam into a body 5 under inspection, and then a reflected echo from an objective region is received by the same group of the transducer elements 1. A signal generated by the received echo is amplified by an amplifier 7 and supplied to a detector 8 which detects a signal corresponding to the amplitude of the echo signal. An output signal from the detector 8 is supplied to a display 9 which performs a luminance modulation for positions corresponding to an ultrasonic beam emitting position and an echo reflected position of the input signal from the detector 8. Thus, a two-dimensional tomographic image of the body under inspection 5 is displayed on the display 9. A series of the above operations is performed under control of a controller 10.
Apart from the above-mentioned electronic linear scan type ultrasonic diagnostic apparatus, there are practically employed such apparatus which make it possible to observe tomographic images of a body under inspection in real time, such as an electronic curved liner scan (convex scan) type ultrasonic diagnostic apparatus, an electronic sector scan type ultrasonic diagnostic apparatus, etc, classified according to ultrasonic beam scan methods. However, either of them can provide only one arbitrary tomographic image of a body under inspection, so that it is necessary to place the probe 2 (see FIG. 18) a different locations or in different directions on the surface of the body to derive information on other sections, thereby complicating handling of the apparatus. Also, the above-mentioned conventional apparatus cannot provide information on two or more sections simultaneously in real time nor three-dimensional or solid information.
To attend to these problems, there is proposed to employ a probe including a so-called two-dimensional array which is formed of multiple small rectangular transducer elements arranged on a plane in two-dimensional directions, wherein a particular one or plural transducer elements are selectively operated to scan an ultrasonic beam in the two-dimensional directions, that is, to transmit and receive the ultrasonic beam in the two-dimensional directions. Such probe employing a two-dimensional array is discussed in IEEE, Trans. Sonics and Ultrasonics, SU-5 (September 1980), on Pages 273 to 280. As shown in FIG. 19, a probe 12 is made up of transducer elements 11 formed by dividing a piezo-electric material into small rectangular portions, and the transducer elements are arranged on a plane in two-dimensional directions. The transducer elements 11 arranged in a plane are each connected to lead wires 13 which in turn are connected to electronic switches 14 arranged in the two-dimensional directions from which a plurality of lead wires extend. The probe 12 of FIG. 19 is constructed such that, by selecting and closing the electronic switches 14 corresponding to the transducer elements 11 belonging to, for example, a particular row L indicated by cross-hatching in FIG. 19, the transducer elements 11 belonging to the particular row L are connected to the lead wires 15.
In this event, the electronic switches 14 may be closed so that a sub-group of the transducer elements group including several adjacent elements 11 solely transmit and receive an ultrasonic beam, and also signals from the transducer elements 11 may be delayed by a phasing circuit 16, so as to provide the ultrasonic beam with a converging effect. Further, the groups of the transducer elements 11 for transmitting and receiving an ultrasonic beam may be sequentially selected by latitudinally stepping the open/close control of the electronic switches 14 to perform an electronic linear scan of the ultrasonic beam. FIG. 20 shows how the electronic linear scan is performed. Specifically, in a probe including small rectangular transducer elements arranged on a plane in two-dimensional directions, an ultrasonic beam A is transferred, for example, along the first row x.sub.1 in the x-direction to perform a first electronic linear scan. Next, the position of the electronic switches 19, shown in FIG. 19 is moved, for example, in the y-direction by a minute distance to transfer the ultrasonic beam A along the second row x.sub.2 in the x-direction, whereby a second electronic linear scan is performed. A two-dimensional scan is achieved by thus sequentially moving such operation in the y-direction by a minute distance to transfer the ultrasonic beam A in the x-direction. Further, by piling up a plurality of ultrasonic tomographic images B in the y-direction, three-dimensional ultrasonic information on a body under inspection can be provided. A reflected echo signal derived by the above-mentioned electronic linear scan is delivered through a signal processing circuit 17 shown in FIG. 19 to a display, not shown.
To achieve a two-dimensional electronic linear scan by the use of the probe 12 including a two-dimensional array shown in FIG. 19, it is required to connect each of the small rectangular transducer elements arranged on a plane in the two-dimensional directions with each of lead wires 13, and also connect each of the lead wires 13 with an electronic switch 14a. Also, to dispose the multiple lead wires 13 and the electronic switches 14a on the rear side of the transducer elements 11, the electronic switches 14a each are required to have a sectional area as small as that of the transducer elements 11. There is proposed, as shown in FIG. 22 a probe in which a group of the electronic switches 14a, formed of a MOS FET integrated circuit including switches Q, is disposed on the rear side of the transducer elements 11, and signal lines 18 for selecting a particular one of the transducer elements 11 by control signals supplied to control terminals Vx.sub.1, Vx.sub.2, Vx.sub.3, . . . and Vy.sub.1, Vy.sub.2, Vy.sub.3, . . . are introduced from the probe to a transmitter 19 and a receiver 20. However, the probe shown in FIG. 22 has a drawback that a plurality of the transducer elements 11 cannot be operated simultaneously.
FIG. 23 shows a more specific construction of the conventional probe schematically shown in FIG. 22. Narrow grooves 22 are cut longitudinally and latitudinally on one side of a large single piezo-electric material 21 to divide the same into multiple small rectangular portions which constitute the transducer elements 11. These transducer elements are each provided on one and the other side thereof with a common electrode 23 and a signal electrode 24 which are opposite with one another. The common electrodes 23 are grounded while the signal electrodes 24 opposite to the common electrodes 23 each have an electrode pad 25 connected to a contact connector 26 through a sound absorbing member 27 which also serves as a support to the transducer element 11. The contact connectors 26 are each connected to a terminal of each of multiple electronic switches 30 formed on a silicon substrate 29 provided on a glass plate 28. The electronic switches 30 each have a control line and a signal output line connected to an external take-out lead 31 though which control and output signals are delivered to the outside.
The conventional probes 12 including a two-dimensional array as shown in FIGS. 19 and 23 require multiple electronic switches 14a or 30 formed of active elements for changing over transmitting and receiving signals supplied to the multiple transducer elements, in which switching noises may cause deterioration in the display quality. Also, since the sound absorbing member 27 (FIG. 23) serves as a support for the integrated circuit of the electronic switches 30 fixed thereon, a soft material or an excessively thin member cannot be employed therefor. Thus, a soft material having a good sound absorbing property cannot be freely selected, which results in insufficient performance of the sound absorbing member 27.